Polybenzimidazoles possess excellent energy resistance and chemical resistance. However, because of the excellent chemical resistance among these properties, for example, excellent solvent resistance, the solubility of polybenzimidazoles in solvents is so low that only solutions having a relatively low polybenzimidazole concentration can be prepared. Further, due to this property, enhancing the viscosity of the solution by increasing the polybenzimidazole concentration is difficult. Therefore, for example, when the polybenzimidazole solution is coated onto a substrate to form a coating, a thick coating cannot be formed without difficulties.
On the other hand, by virtue of their properties, polybenzimidazoles are expected to be utilized in semiconductor production devices and the like. Specifically, the covering of the production device on its surface formed of a metal or the like with a polybenzimidazole coating can protect the production device and, at the same time, can prevent the semiconductor device, to be produced, from being brought into contact with a metal, whereby the contamination of the semiconductor device with impurities can be prevented. As described above, however, difficulties are encountered in forming a satisfactorily thick coating by coating of the polybenzimidazole solution. In order to solve the above problem, the incorporation of a metal solubilizer has also been studied. However, this method also cannot significantly improve the solubility of polybenzimidazoles and, in addition, is disadvantageously causative of the inclusion of metallic impurities.